This invention relates to a radiant beam exposure apparatus and particularly an electron beam exposure apparatus in which a workpiece is exposed to an electron beam controlled by a deflection signal and a blanking signal which has been generated in response to an information signal corresponding to a desired pattern.
In a prior art electron beam exposure apparatus a workpiece to be exposed is mounted on a workpiece supporting platform or a carriage and the projection of the electron beam is turned ON and OFF in synchronism with the deflection scanning of the beam so as to form a predetermined pattern on one block of the workpiece. Then, after moving the carriage one step the same produce step is repeated thereby forming a predetermined pattern on the entire surface of the workpiece.
The pattern to be finally obtained by the electron beam exposure apparatus of the type referred to above has a dimension of about 50 mm .times. 50 mm, for example. However, the area that can be efficiently scanned by the electron beam is less than several millimeter square so that in order to obtain a pattern having the desired area as above described it is necessary to join together a plurality of small scanning pattern blocks each having an area of several millimeter square.
Where the workpiece thus prepared is to be used as a mask for manufacturing a large scale integrated circuit the pattern should have an extremely high dimensional accuracy. The maximum permissible errer at such high accuracy is about 0.5 micron. In an electron beam scanning apparatus, the electron lens system utilized therein has an aberration which increases in proportion to two or three power of the number of patterns to be formed. For this reason, when one side of the block has, for example, a length of 5 mm, an errer of the order of 5 microns would be resulted causing it difficult to accurately join together respective blocks. Accordingly, the resulting pattern will be considerably deformed. In order to obtain a pattern having a dimension of 50 mm .times. 50 mm by assembling together a plurality of blocks each having a dimension of 0.5 mm .times. 0.5 mm it is necessary to join together (50/0.5).sup.2 or 10.sup.4 blocks. In this case, when a pattern of one block has been formed the carriage is moved 0.5 mm to the next scanning block, and it takes about one second for this shift. Accordingly, until all of 10.sup.4 blocks are formed it takes 10.sup.4 seconds, that is several hours. This greatly decreases the merit of using the electron beam designed for high speed exposure, hence the commercial value of the apparatus.
When forming a desired pattern on the workpiece by scanning an electron beam the accuracy of describing the pattern is not so high as the accuracy of the characteristic of the deflection current supplied to the scanning and deflection coils but it is extremely difficult to oscillate the electron beam at a frequency of several tens KHz and to control without any drift and at an accuracy of higher than 10.sup.-3 the current amplitude which varies from time to time. For this reason, it is desirable that the length of one side of each block should be less than 0.2 mm.
While in the conventional electron beam exposure apparatus the deflection and blanking control of the electron beam is effected in synchronism with a predetermined clock pulse, the carriage is driven by a servo-mechanism controlled in synchronism with the clock pulse. For this reason, for the purpose of synchronizing the moving speed of the carriage and the pattern forming speed or the beam scanning speed during the forming of a pattern by the electron beam the speed of the carriage is detected by a laser interferometer so as to correct the speed of the carriage by a signal detected by the interferometer.
In correcting the movement of the carriage it is necessary to correct not only the speed of the carriage but also the angular displacement thereof with reference to the movements in the direction of X and Y axes. Since such corrections should be made at high accuracies it is necessary to use highly accurate correction device for the carriage.